1. Field of the Invention
The present invention relates to a network system incorporating a plurality of buses each of which is constituted by connecting a plurality of nodes to one another with communication-control signal lines each of which is capable of transmitting a control signal and an information signal in a mixed manner, and to a bridge apparatus for connecting the buses to one another.
2. Related Background Art
Network systems have been widely used that are constituted by connecting a multiplicity of computers, peripheral equipment or AV apparatuses to one another. Each of the apparatuses which are connected as described above is called a "node" which includes an interface for establishing the connection with the other apparatuses.
The structure of the conventional network system is shown in FIG. 1. The network system shown in FIG. 1 is constituted by connecting eleven buses 100 to 110, each of which is formed by connecting a plurality of nodes to one another with communication-control signal lines, to one another by bridges 90 and 91 for example.
The communication-control signal lines may be signal lines of a type based on IEEE1394 which is a standard for serial interfaces. Not more than sixty three nodes can be connected to one bus because of the regulation of IEEE1394. If a larger number of nodes must be connected, a plurality of buses must be prepared to connect the buses to one another with the bridges 90, 91 and so forth. IEEE1394 defines a fact that a large-scale network system can be constituted by not more than 1023 buses. Moreover, IEEE1394 defines a fact that determination of states of the connection among the buses and assignment of identification (ID) numbers for the buses are automatically performed. The process for assigning the ID for the bus is called a configuration process. The configuration process is performed when a bus is added or omitted, the configuration process being performed in the overall network system.
If the number of the buses is increased, addition and omission of the buses are performed frequently. Whenever the addition or the omission is performed, the configuration process must be performed in the overall network system. Therefore, interruption of data communication frequently occurs. What is worse, there is apprehension that the apparatus is operated incorrectly or data is eliminated. Since the computer and peripheral equipment must have significant reliability, frequent configuration processes undesirably cause the operations of the apparatuses to be unstable.
In a case of a large-side network system having a multiplicity of buses, there is a possibility of using, to connect the buses to one another, a line connection type communication passage, such as the public telephone network, or a wireless communication. The communication passages of the above-mentioned types suffer from unstable connection and easily encounter occurrence of unintentional connection and disconnection. In the above-mentioned case, there is a possibility that configuration is frequently repeated. Thus, there is apprehension that the network system becomes unstable.
If the apparatus, for example, the node or the bridge, breaks down or becomes defective, the network system cannot always be operated in conformity with the foregoing standard. Also the foregoing fact causes the operation of the network system to be unstable.